The preparation of high quality coffee beverages has been well known in commercial coffee shops for many years. Throughout the years methods of making coffee have been refined and skilled people trained to produce the best coffee beverages. There has been rapid growth, particularly in the last 10 years, of coffee shops offering more specialist drinks such as espresso and cappuccino. These types of beverages have historically been regarded as luxury items because of the need for expensive, complex machines capable of producing the high pressures necessary for making them. Such machines have to be properly operated and maintained by a trained barista to produce good quality.
Consumers' tastes for high quality coffee beverages has not only increased demand for luxury top quality beverages from specialist coffee shops, it has also led to a desire for a greater variety of speciality beverages, and the ability to make such beverages in the comfort of one's own home.
Domestic filter coffee machines have been widely available since the 1960s. However, such machines are not able to produce espresso style coffee, nor foamed milk required for the preparation of speciality drinks such as cappuccino. Domestic coffee machines have developed significantly since the introduction of the first filter machines and are now essential pieces of kitchen equipment in many households. Some such machines dispense individual servings of a beverage directly into a drinking receptacle, and derive the beverage from a bulk supply of beverage ingredient or from individual packages of beverage ingredient such as pods, pads or cartridges. In the following specification, such packages will be referenced by the general term cartridges. Machines which use such cartridges eliminate the need for cleaning and can enable the user to make a selection of beverages. An example of one type of such cartridge is described in EP-A-1440903. The beverages are formed from brewing, mixing, dissolving or suspending the beverage ingredients in water. For example, for coffee beverages, heated water is forced through the cartridges to form the extracted solution. The use of cartridges in such machines has become increasingly popular due to their convenience and the quality of the beverage produced.
An example of a machine for preparing beverages using this type of cartridge is described in EP-A-1440644. This type of machine provided an improvement over the prior art known at the time in that it operated at a lower pressure than the previously known machines, which were designed for the commercial or industrial markets rather than the domestic market. Hence it was more suitable for the domestic market in terms of cost, reliability and performance.
Despite the advances made in domestic coffee machines and associated cartridges, there continues to be a demand for ever better barista quality coffee beverages which can be readily prepared in the home without the need for specialist equipment or training.
To allow a user to produce a full range “coffee shop” style beverages in the home it is not only necessary to provide means for brewing high quality espresso type coffee, it is also necessary to provide the user with means for producing foamed milk to make beverages such as cappuccino. Traditionally foamed milk has been produced in coffee shops by using a steam wand to direct a steam jet into a reservoir of milk. This is still the primary method of producing foamed milk in a commercial environment. However, it is inconvenient to use steam jet equipment in the home since it can be dangerous if not used correctly and can also be difficult to clean. This is particularly disadvantageous for equipment used with milk which requires thorough cleaning to prevent contamination.
An example of a cartridge for a domestic beverage machine which is suitable for producing foamed milk is known from EP-A-1716055. Foamed milk is produced from the cartridge by causing air to become entrained in a milk stream produced when water is mixed with a concentrated milk ingredient contained within the cartridge. This is achieved by passing milk through an eductor within the cartridge. The eductor comprises an aperture which is arranged to produce a jet of milk. The jet of milk passes over an air inlet causing air to become entrained in the milk thereby creating foamed milk. Foamed milk produced from such cartridges allows coffee shop style beverages, such as cappuccino, to be readily produced in the home without the need for potentially dangerous, and difficult to clean, steam wand equipment. It is desirable to continue to develop such cartridges to further improve the quality of foamed milk which may be produced in the home.
Investigations have shown that elongate agglomerate particles form in the concentrated liquid milk ingredient of the cartridges during processing and storage. These particles have the potential to block, or partially block, the aperture resulting in less air being entrained in the milk stream. If this happens, the quality and quantity of the foamed milk can be adversely affected.
It is known to use filters in cartridges for beverage machines to prevent particulate matter from reaching the outlet of the cartridge and thus contaminating the beverage. Filters are, for example, commonly employed in cartridges for the production of coffee as described in EP-A-1440903 referenced above. Such filters comprise a plurality of fine openings which are smaller than the smallest dimension of the particulate matter to be filtered. This has the effect of preventing fine particulate matter from reaching the outlet of the cartridge. However, it also has the effect of restricting the flow of beverage through the cartridge as particulate beverage ingredient builds up on the upstream side of the filter. Such flow restriction is not desirable in cartridges used for the production of foamed milk since flow restriction reduces the efficacy of the eductor and consequently reduces the quality and quantity of the foamed milk produced. This is in direct contrast to the desired effect of improving foam quality and quantity.